Thread: Pharmacology - Review Questions

1. If a drug is highly bound to plasma proteins, it

A. has a large volume of distribution
B, has a high renal clearance
C. is a likely candidate for drug interactions
D. is most likely carried by alpha-glycoprotein
E. is a quaternary ammonium salt

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Answer / Explanation:

[HIDE]Answer: C. Drugs with extensive plasma protein binding usually have low vd values (recall vd= dose/C deg.and slow renal elimination because only the free fraction is filtered. Albumin is the major plasma protein to which drugs bind, and the constant positive charge on quaternary amines prevents their binding to plasma proteins. Competition between drugs for plasma protein binding sites can lead to drug interactions(e.g. the displacement of warfarin by sulfonamides may increase its anticoagulant effects).[/HIDE]

2. Most drugs gain entry to cells by

A. passive diffusion with zero-order kinetics
B. passive diffusion with first-order kinetics
C. active transport with zero-order kinetics
D. active transport with first-order kinetics
E. passive diffusion through membrane pores

Answer / Explanation:

[HIDE]
Answer: B. The permeation of most drugs through cellular membranes is by the process of passive diffusion, a nonsaturable process that follows first-order kinetics. Concentration gradient and lipid solubility of the drug are important determinants of the rate of diffusion.
Only a fewdrug molecules are substrates for active transport processes (e.g,tubular secretion of beta-lactam antibiotics); these are saturable at high concentrations. Only very small ions or drugs ethanol) may penetrate bioinembranes via aqueous pores.
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3. In the case of a drug that follows first order elimination,

A. the rate of elimination is constant
B. the elimination half-life varies with the dose
C. the volume of distribution varies with the dose
D. the clearance varies with the dose
E. the rate of elimination varies directly with the dose

Answer / Explanation:

[HIDE]
Answer:E. In first-order kinetics, the elimination rate of a drug is directly proportional to its plasma concentration, which in turn is proportional to the dose. Drugs that follow first-order elimination have a constant elimination half-life. Likewise, clearance and volume of distribution are pharmacokinetic characteristics of a drug that do not routinely change with dose, although they may vary in terms of disease or dysfunction.
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